In inserting a recording medium, i.e., a disk, into an optical-disk-drive (ODD) unit mounted in an electronic apparatus, the disk may be misinserted into a gap or the like produced between, for example, the ODD drive unit and a casing of the electronic apparatus. To prevent such misinsertion, there are some electronic apparatuses such as an apparatus whose casing has a rib provided in the gap and an apparatus having a sponge or the like provided in the gap.
Among such structures that prevent the misinsertion of a disk into the drive unit, there is a typical technique in which a recess is provided in a tray for conveying a disk cartridge and a projection corresponding to the recess is provided on a casing of the apparatus, where the projection is configured to fit into the recess.